package org.bouncycastle.asn1;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.bouncycastle.util.Arrays;

public class DERBitString extends ASN1Object implements DERString {
    private static final char[] table = { '0', '1', '2', '3', '4', '5', '6',
            '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

    protected byte[] data;
    protected int padBits;

    /**
     * return the correct number of pad bits for a bit string defined in a 32
     * bit constant
     */
    static protected int getPadBits(int bitString) {
        int val = 0;
        for (int i = 3; i >= 0; i--) {
            //
            // this may look a little odd, but if it isn't done like this pre
            // jdk1.2
            // JVM's break!
            //
            if (i != 0) {
                if ((bitString >> (i * 8)) != 0) {
                    val = (bitString >> (i * 8)) & 0xFF;
                    break;
                }
            } else {
                if (bitString != 0) {
                    val = bitString & 0xFF;
                    break;
                }
            }
        }

        if (val == 0) {
            return 7;
        }

        int bits = 1;

        while (((val <<= 1) & 0xFF) != 0) {
            bits++;
        }

        return 8 - bits;
    }

    /**
     * return the correct number of bytes for a bit string defined in a 32 bit
     * constant
     */
    static protected byte[] getBytes(int bitString) {
        int bytes = 4;
        for (int i = 3; i >= 1; i--) {
            if ((bitString & (0xFF << (i * 8))) != 0) {
                break;
            }
            bytes--;
        }

        byte[] result = new byte[bytes];
        for (int i = 0; i < bytes; i++) {
            result[i] = (byte) ((bitString >> (i * 8)) & 0xFF);
        }

        return result;
    }

    /**
     * return a Bit String from the passed in object
     * 
     * @exception IllegalArgumentException
     *                if the object cannot be converted.
     */
    public static DERBitString getInstance(Object obj) {
        if (obj == null || obj instanceof DERBitString) {
            return (DERBitString) obj;
        }

        throw new IllegalArgumentException("illegal object in getInstance: "
                + obj.getClass().getName());
    }

    /**
     * return a Bit String from a tagged object.
     * 
     * @param obj
     *            the tagged object holding the object we want
     * @param explicit
     *            true if the object is meant to be explicitly tagged false
     *            otherwise.
     * @exception IllegalArgumentException
     *                if the tagged object cannot be converted.
     */
    public static DERBitString getInstance(ASN1TaggedObject obj,
            boolean explicit) {
        DERObject o = obj.getObject();

        if (explicit || o instanceof DERBitString) {
            return getInstance(o);
        } else {
            return fromOctetString(((ASN1OctetString) o).getOctets());
        }
    }

    protected DERBitString(byte data, int padBits) {
        this.data = new byte[1];
        this.data[0] = data;
        this.padBits = padBits;
    }

    /**
     * @param data
     *            the octets making up the bit string.
     * @param padBits
     *            the number of extra bits at the end of the string.
     */
    public DERBitString(byte[] data, int padBits) {
        this.data = data;
        this.padBits = padBits;
    }

    public DERBitString(byte[] data) {
        this(data, 0);
    }

    public DERBitString(DEREncodable obj) {
        try {
            this.data = obj.getDERObject().getEncoded(ASN1Encodable.DER);
            this.padBits = 0;
        } catch (IOException e) {
            throw new IllegalArgumentException("Error processing object : "
                    + e.toString());
        }
    }

    public byte[] getBytes() {
        return data;
    }

    public int getPadBits() {
        return padBits;
    }

    /**
     * @return the value of the bit string as an int (truncating if necessary)
     */
    public int intValue() {
        int value = 0;

        for (int i = 0; i != data.length && i != 4; i++) {
            value |= (data[i] & 0xff) << (8 * i);
        }

        return value;
    }

    void encode(DEROutputStream out) throws IOException {
        byte[] bytes = new byte[getBytes().length + 1];

        bytes[0] = (byte) getPadBits();
        System.arraycopy(getBytes(), 0, bytes, 1, bytes.length - 1);

        out.writeEncoded(BIT_STRING, bytes);
    }

    public int hashCode() {
        return padBits ^ Arrays.hashCode(data);
    }

    protected boolean asn1Equals(DERObject o) {
        if (!(o instanceof DERBitString)) {
            return false;
        }

        DERBitString other = (DERBitString) o;

        return this.padBits == other.padBits
                && Arrays.areEqual(this.data, other.data);
    }

    public String getString() {
        StringBuffer buf = new StringBuffer("#");
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();
        ASN1OutputStream aOut = new ASN1OutputStream(bOut);

        try {
            aOut.writeObject(this);
        } catch (IOException e) {
            throw new RuntimeException("internal error encoding BitString");
        }

        byte[] string = bOut.toByteArray();

        for (int i = 0; i != string.length; i++) {
            buf.append(table[(string[i] >>> 4) & 0xf]);
            buf.append(table[string[i] & 0xf]);
        }

        return buf.toString();
    }

    public String toString() {
        return getString();
    }

    static DERBitString fromOctetString(byte[] bytes) {
        if (bytes.length < 1) {
            throw new IllegalArgumentException("truncated BIT STRING detected");
        }

        int padBits = bytes[0];
        byte[] data = new byte[bytes.length - 1];

        if (data.length != 0) {
            System.arraycopy(bytes, 1, data, 0, bytes.length - 1);
        }

        return new DERBitString(data, padBits);
    }
}
